Pulse forming network



Sept. 15, 1959 J. RoMANELLl PULSE FORMING NETWORK Fil'ed June 25, 1958 SPM 3J. 9m

United States Patent Oiiice Patented Sept. 15, 1959 PULSE EoRMING ruiTWoRKh John" Romanelli, Eullerton, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Application June 25, 1958, Serial No( 7745,'796y 3 Claims. (CL 3074-106) The present invention relates to a device for generating a particular type of pulse andmore particularly to apparatus for generating pulses having a desired energy distribution and time duration which pulses are of a predetermined waveformt In accordance with the present invention, a'plurality of inductance-capacitance branches having parameter values which represent the odd harmonics1 of avFourier expansion are discharged into a corresponding number of primary windings of a'pulse'transformer. This pulse transformer possesses a single output winding which is poled in a manner relative to the primary windings to produce an algebraic sum ofV the aforementioned odd harmonics thereby to produce pulse waveforms described by the trigonometric function, cos2 wt.

It is therefore an object" ofthe present invention to provide an improved apparatus for generating pulses each having a predetermined energy distribution and time duration.

Another object of the inventio'nis to provide apparatus for simultaneously generating a plurality of' electrical :signals representative of selected' Fourier components :and effectuating the algebraic sum ofthe. components to `produce a pulse having a predetermined energy' distribution and time duration.

Still another object of the invention is to providel ap'- paraus for simultaneously generatingelectric' wave signals representative of the iirst and third Fourier components -of a pulse having a waveform described by cos2 wt and Acombining the electric wave signals to produce a pulse `of a waveform substantially describedby cos2' wt.

The above-mentioned and other features and objects 'of this invention and the manner of obtaining themwill become more apparent by'referenceto the followinlg'de- `scription taken in conjunction with the accompanying A4drawings, wherein:

Fig. l illustrates a schematic circuit diagramy of the :apparatus of the present invention; and

Fig. 2 shows the manner in which the Fourier com- ;ponents are combined to produce the pulse havinga wave- 'iform described by cos2 wt.

There is illustrated a preferred embodiment of the :apparatus of the present invention, which apparatus comprises a pulse-formingvnetwork 10 that is'ladaptedfto :be discharged through a pulse transformer 12.' into a load 14 by means of a switch tube 16 which may; for example, be a hydrogen thyratron. The tube 16 includes a plate 17, a control grid' 18 andy aVA cathode 19,v the plate 17 being connected toan input'termin'all 20` of the pulse forming network 10 and the cathode 19-be`- ing connected to ground. The switch tube 16 is rendered conductive by the application of a trigger pulse 21 to a trigger input terminal 22, whereupon the trigger pulse .Z1 is coupled through a low pass lter 23 to the control grid 18 of the switch tube 16. The purpose of the low pass lter 23 is to prevent the momentary rise in Ygrid potential prior to the grid cathode space being ion- .ized from reaching the source of trigger input pulses.

The pulse forming network 10 is charged by way of example by means of a source Z4 of high voltage direct current potential, `negative terminal of which is referenced to ground and the positive terminal of which is connected through a charging inductor 26 and an isolating diode 28 to theinput terminal 20 of the pulse formingnetwork 10.

More particularly, the pulsel forming network 10 includes-impedance branches 30, 31 and 32 connected from the'nput terminal 20 to output terminals 33, 34and 35, respectively. In the present case, each of the impedance branches 30, 31 and 32 are used to generate'the first, thirdand nth harmo-nic of a pulse having a waveform described by cos2 wt. In particular, the impedance branch 30 constitutesthe series combination of inductor L1 and capacitor G1 connectedin seriesY combination between the input' terminal 2t) and the output terminal 33; the impedanee branch131 constitutes an inductor L3 and a capacitor C3A connected` in series combination between the input terminal 20 and the outputV terminal 34 and the impedance branch`32constitutes an inductor LI1 and acapacitor Cn connected in series combination from the input terminal 20 to the output terminal 35 of the pulse forming network 10. In accordance with the present invention,- it is essential that the values of the aforementioned inductorsand capacitors be determined in accordance with the following relations so that electrical signalsof the proper harmonicfand of the desired amplitude may begenerated;

Inraddition to the above, to is the width at the base of the waveform of the pulse to be generated, RI, is the resistance of the load resistor 14, and A is the'secondary winding toprimary winding turns ratio of the pulse transformer 10.

In the apparatus of the present invention, it has been found that theimpedance branches 30, 31 which generate: the rst and third harmonic components, respectively; of' the Fourier series produce a substantially accurate'reproduction of a pulse having a waveform described by cos2 wt. Referring to Fig. Z, there is shown the manner in which the rst harmonic 40 is combined with Vthe third harmonic 42' signal, both of which are illustrated by a dashed line, are combined'to produce the cos2 wt waveform. 44illustrated by a solidline'. In particular, the rst and third harmonics 42 are generated sovthat theyfc'ommenc'e simultaneously,.the tir'strh'armonic 40 making a positive alternation iirst while the third harmonic 42, on the other hand, commences with a negative alternation. A combination of the first and third harmonics 40, 42 produces the waveform 44 which, as previously specied, is substantially described by cosZ wt.

Referring again to Fig. l, the parameter of the mpedance branches 30, 31 are chosen as follows to gen erate a cos2 wt pulse 44:

L1=0.339 to R0 henrys L3=0.623 ta Ra henrys is 01:0.245 -R-o farads 03:0.01795 lf3-0 ramas wherein t is expressed in seconds and Ro is expressed in ohms. In choosing a value for to, consideration is given to the desired width of the pulse at, for example, 70% of its peak power level. In the event that it is desired that the pulse be 20 miscroseconds wide at 70% of the peak power level, the base width, to, for a pulse having a waveform described by cos2 t would be approximately 55 microseconds.

Also, in accordance with the invention, each output terminal 3-3, 34 and 35 is connected to one terminal of a separate primary windings 46, 47 and 48, respectively, of the pulse transformer 10, the remaining terminal of each primary winding being referenced to a point of substantially fixed potential such as, for example, ground. Each of the primary windings 46, 47 and 48 have the same number of turns about a common core so that the ratio of the number of turns in a secondary winding 50 to the number of turns in each of the primary windings 46, 47 and 48 is the same in each instance, whereby each harmonic signal will retain its same relative magnitude across the load resistor 14. Also, the primary windings 46, 47 are poled relative to the secondary winding 50 as indicated in the drawing so as to combine the ndividual electrical waveforms 40, 42 in the manner specified in connection with the description of Fig. 2.

What is claimed is:

l. A pulse generating apparatus comprising a pulse forming network having an input terminal and first and Ifarads, respectively, thereby to produce the fundamental second output terminals, said network including a first i impedance branch connected from said input terminal to said first output terminal adapted to produce the fundamental Fourier component of a predetermined pulse waveform and a second impedance branch connected from said input terminal to said second output terminal adapted to produce the third harmonic Fourier component of said predetermined pulse waveform; a pulse transformer having first and second primary windings connected from said first and second output terminals, respectively, of said network to a terminal maintained at a substantially fixed potential and a secondary Winding connected across a load impedance, said first and second primary windings and said secondary winding being disposed about a com-mon core and poled to produce a signal representative of the algebraic sum of said Fourier components; means coupled to said input terminal of said pulse forming network for simultaneously charging said first and second impedance branches; and means responsive to trigger pulses connected from said input terminal of said pulse-forming network to said terminal duce the fundamental Fourier component of a predetermined pulse waveform and a second inductor and a second capacitor connected in series combination from said input terminal to said second output terminal, the values of the respective parameters of said second inductor and second capacitor being adapted to produce the third harmonic Fourier component of said predetermined pulse waveform; a pulse transformer having first and second primary windings connected from said first and second output terminals, respectively, of said network to a terminal maintained at a substantially fixed potential and a secondary winding connected across a load impedance, said first and second primary windings and said secondary winding being disposed about a common core and poled to produce a signal representative of the algebraic sum of said Fourier components; means coupled to said input terminal of said pulse forming network for simultaneously charging said first and second capacitors; and means responsive to trigger pulses connected from said input terminal of said pulse-forming network to said terminal maintained at said substantially fixed potential for discharging said vfirst and second capacitors of said network thereby to generate pulses having said predetermined waveform across said load impedance.

3. A pulse generating apparatus comprising a pulse forming network having an input terminal and first and second output terminals, said network including a first inductor and a first capacitor connected in series combination from said input terminal to said first output terminal, the Values lof the parameters of said first inductor and first capacitor being substantially equal to 0.339 tR0 henrys and i@ 0.245 R-o lnation from said input terminal to said second output terminal, the values of the parameters of said second inductor and second capacitor being substantially equal to v0.623 1Ro henrys and tu 0.01795 U farads, respectively, thereby to produce the third har- .monic Fourier component of said predetermined pulse Waveform; a pulse transformer having first and second primary windings connected from said first and second output terminals, respectively, of said network to a terminal maintained at a substantially fixed potential and a secondary winding connected across a load impedance, said first and secondary primary windings and said secondary Winding being disposed about a common core and poled ina manner to produce a signal representative of the algebraic sum of said Fourier components; means coupled to said input terminal of said pulse forming network for simultaneously charging said first and second capacitors; and means responsive to trigger pulses connected from said input terminal of said pulse-forming network to said terminal maintained at said substantially fixed potential for discharging said first and second capacitors of said network thereby to generate pulses having waveforms substantially described by cos2 wt across said load imped ance,

No references cited,

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